<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>hello world</title>
</head>
<body>
    <!-- script里面默认可以放很多种语言，现在默认是JS -->
    <!-- 外部式引入js文件 -->
    <script src="hello.js"></script>
    <!-- <button onclick="alert('hello world!')">这是一个按钮</button> -->
    <script>
        // alert('hello world!');
    </script>
    
</body>
</html>